1. Field of the Invention
The present invention relates to a method of measuring the density of a visible region of a beam of light reflected from a planar image.
2. Description of the Related Art
Conventionally, in order to detect the density at a predetermined position (hereinafter referred to as the detection position) of a planar image recorded on a recording material, a beam of light is radiated from above the detection position, and the quantity of the light beam reflected from the image is detected by an RGB sensor. The RGB sensor has three photosensors provided with red (R), green (G), and blue (B) filters, respectively.
Since a current value i detected by the photosensors and the quantity of light are in direct proportion to each other, the quantity of light can be readily calculated from the measured current value i. In addition, the quantity of light and density D of the image are in the relationship shown below. EQU Density D=log.sub.10 (I.sub.0 /I) (1)
where PA0 I.sub.0 : intensity of incident light PA0 I: intensity of reflected light
Accordingly, the density can be determined from the quantity of light radiating from a light source and the quantity of light calculated from the detected current value.
However, in cases where the density is measured as described above, an angle between the incident light radiated from the light source and the light reflected from the planar image recorded on a recording material, as well as an angle between the reflected light made incident upon the RGB sensor and a perpendicular direction (normal) to a detection surface of the RGB sensor are not necessarily constant but instead are dependent on the detection positions. As these angles vary, the detected value also varies, thereby making it impossible to effect the measurement in a stable manner. For this reason, an attempt has been made to minimize the aforementioned angular changes at each detection position through a mechanical means employing a tool such as a micro-tracer using a ball screw. With such an arrangement, however, a rise in the product cost is unavoidable.